Analog-to-digital converters (ADCs) have traditionally been fabricated using electronic integrated circuits. The function of an ADC is to repeatedly sample a time-varying analog waveform, generally at fixed time intervals, and to generate a digital representation of the analog waveform with a certain level of precision. The precision of electronic ADCs, however, is currently limited to an effective number of bits (ENOB) of 8.5 at 2 GHz RF bandwidth, and decreases with increasing frequency.
Optical ADCs promise to overcome the limitations of electronic ADCs and to provide an improved speed and resolution for the digitization of analog waveforms at very high frequencies greater than about 10 GHz. There are many different and varied types of optical ADCs known to the art which have been summarized in a recent review article by G. C. Valley entitled “Photonic Analog-to-Digital Converters” published in Optics Express, vol. 15, paper no. 75372, 5 Mar. 2007. Various types of optical ADCs are also disclosed in the following U.S. Pat. Nos. 4,058,722; 4,928,007; 6,292,119; and 6,326,910; and in U.S. Statutory Invention Registration No. H353.
The present invention provides an advance in the art of optical ADCs by providing an optical ADC which can be made to be all-optical in that it can receive an optical analog input signal and convert this signal into an optical digital output signal.
The optical ADC of the present invention can be formed as a photonic integrated circuit (PIC) which provides each bit of the optical digital signal spatially separated so that each bit of the optical digital signal can be directed into a different optical fiber for parallel data transmission. Alternately, an optical waveguide combiner can be provided in the optical ADC or as a separate PIC for use with the optical ADC to generate a serial optical output by interleaving the various bits of the optical digital signal.
These and other advantages of the present invention will become evident to those skilled in the art.